Stability does my motor write checks the bicycle can't cover?

[David Jackson]

Hi Mike;

I find I quite like my newly built 113" motor; I really like the powerband which is completely different from the SE 264 cams' powerband. The cams in my motor now are gear drive Wood 408G which give nice power at lower rpm which is what I think Harleys should have; plus lower rpm = lower piston speed and theoretically more longevity; isn't that right? (I hope so!)

However, and this is a big however; even though I don't really hotrod the bike; no wheelies, no burnouts, none of that sort of thing; when I get on the gas this bike easily gets to 100 mph and more right away it seems. When it gets there it becomes unstable.

I noticed it today; after stopping for a root beer I hopped on the bike and sort of chased/caught up to a fellow who had left a few minutes previously and I noticed the speedo said about 105 mph and the front end was going from side to side ever so slightly. I loosened my grip on the bars in case I am doing that but it really made no difference so I slowed down to 95 or so and there the bike is much better.

I am using Metzeler ME 880 tires and I suspect them. My tire pressure may have been 1 pound below spec (44 rear and 38 front, measured about 3 hours after the bike was parked). I wonder if these tires are really safe for our bikes or if something else could be wrong.

When the bike was at the dealer's for the engine work I complained about this instability and I think the frame/swing arm/steering head bushings were all checked and I had a Sputhe engineering gadget installed (that makes the bike more stable in medium speed corners and the like I think).

I really don't need to go any faster than 120 or so but I would like my bike to be safe and stable at that speed; which speed I would not see very often. Like most of us I do most of my riding between 50 and 90; but I don't like the idea that my bike is unsafe at higher speeds.

What might your thoughts be on this one? Bike is a 2001 FXDXT and I ride it with the stock handlebar mounted fairing, the stock HD short windshield, the stock HD saddlebags, and a small rear bag on the stock HD luggage rack (one of those cylindical ones).

Regards;

David Jackson

[Mike]

I was going to mention the True-Trak stabilizer but you've already got the Sputhe Posi-trak (assuming) which does the same. Typ. strg head oscillations are a function of something in the rear of the bike (i.e., loose swingarm, deflated tire, too much weight in the saddlebags, etc.). We've been told of similar issues with V-rods at high speed and it took H-D a while to figure it out (thinking along the lines above). It turned out to be the front tires. Some were "cupped" do to hard braking and others were run underinflated for long periods, possibly weakening the sidewalls and other tire structures. It was found that new front tires curred the problem in each case even though the tires removed, in many cases, appeared just fine. Since you are not running spec. tires, we cannot comment on their effect, that woud be a question for the manufacturer. Since your local shop has done all the things we would do I'm at a loss for what to suggest. Sometimes running the strg head bearings on the tight side can help (sim. to a strg dampner) but a weave could be introduced if too tight. Possibly a steering dampner from Pingle or other would help. Advise to get a good one, these are very much a "you get what you pay for" item. Good ones are not cheep but remarkable in their performance.
Thanks, Mike

[David Jackson]

Hi Mike;

The True Track Stabilizer; does that install at the rear of the motor? I think I have heard of that part for Electra Glides but I am not sure.

I gather from your comments that you have no experience with Metzeler ME 880s being the source of a handling problem though you did mention spec tire; I presume you mean Dunlops with HD branding? Apparently there are two kinds of Dunlops with HD branding I could run; the stockers and a slight upgrade. Is there any chance the slight upgrade will be an improvement? What kind of experiences have you heard of from users of those tires?

Cupping the tires; I can't see any. Hard braking; I do have two discs of course, I went to the HD stainless lines and the floating rotors with some aftermarket pucks and I do get very good braking performance from that set up. I don't know that I have skidded the tire or anything like that; but I do ask the brakes to really stop at times and these do a pretty good job of that. (I would not want a powerful motor with just one disk!)

Tire underinflation; possibly yes but not by very much. When I got the tires the brochure said 40/38; when I checked the Metzeler website yesterday it said 44/38. I may have underinflated the tires by a pound or two, or that is to say they may have lost a pound or two's worth of air; but I don't really know how accurate all tire pressure guages are, that is if they are accurate within 1 pound or +/- 5 pounds or something like that.

I don't have very much weight in the saddlebags; but I can check to see just how much.

Of course, as you said, sometimes the take off tires show no visible sign of any problems but by replacing them the handling is improved. I don't recall this handling problem with my stock HD Dunlops though my motor was stock when I had them; I did get to 110 mph once and the bike was stable as I recall.

Thanks for the steering damper suggestion; where would I get one of those?

I don't want to sound like a compete "speed demon" because I am not but I do want to find a way to have a safe handling bike. I will write to Metzler but I know what they will say; "There is nothing wrong with our tires, properly inflated they are the best in the world" etc. etc.

I might also talk to Sputhe.

Tell me a little more about a weave introduced by too tight steering head bearings if you would be so kind. When would that weave happen, slow speeds or high, corners or straights, that sort of thing.

Regards;

David Jackson

[Mike]

The weave will be on straights. It's like the bike will not want to continue to go where pointed so constant corrections have to be made to keep it going straight. Either Pingle Enterprises or Storz Performance will be a good source for dampners. Underinflated tires typ. would be like running at 20lbs. (or 10lbs under recommendations).
The Posi-trak installs on both the front and rear motor mounts, the True-trak is on the rear only.
I' talked with some other techs here and have come up with some other possibilities. Has the bike been lowered in either the front or rear or both? Lowering the rear only has been known to cause sim. problems by changing the fork angle and weight distribution (bias). Are the shocks and front forks stock? Stock rear shocks are not very good at damping and rebound and can cause a twisting action on the swingarm (especially with bike ci motors) thus causing strg head oscillations. The same is somewhat true of the front forks. Dyna/FXR front ends are notoriously soft and have a lot of travel which can also lead to a twisting and "pogo-ing" motion. I've always liked Metzler tires and doubt that it is a tire problem, so long as the tires are known to be in good shape and undamaged in any way.
Suggestions; If the bike is lowered in the rear, then lower the front the same amount to regain strg head angle and weight bias. Whether lowered or not, installing Works Performance rear shocks (special order only and built to specs), RaceTec emulators in the front forks and front fork brace (HD) will not only take care of the handling issue but greatly improve the ride quality.
Thanks, Mike

[David Jackson]

HI Mike;

Many thanks for those ideas!

I don't know where to get RaceTec emulators. I do know where to get Works Performance shocks; but as the built to specs comes in I am probably too ignorant to know exactly what to ask for. Perhaps some tech people there can help.

I do have an SE fork brace on the bike; one of the first things I did a couple of years ago. It is nice and shiny! Are there better braces?

Getting to the obvious; I just (finally) checked the tread depth on the rear tire and found it is 3/32 of an inch. The service manager at my local dealership recommends changing rear tires at 2/32 so 3/32 is getting close. I keep thinking of my "new" tires and I guess they aren't any more. I am planning to use the upgraded HD Dunlops this time.

Speaking of lowering the rear; would not that tend to increase rake and make the bike more stable in a straight line? I had a Jim Belland frame back in 1972 with a big inch CH motor; 19" wheels front and rear and it was unstable at high speeds. I took the bike to Bonneville after changing to an 18" wheel in the rear, with struts, and the bike was safe as could be. It went 141 mph there. That made me think that maybe I should lower my shocks to the lowest notch and maybe that will help. They were in the middle. The damper clicker was set to almost the hardest setting but if the shocks aren't all that good that may well not be enough.

The shocks, wheels, and forks are all stock.

As to front fork assemblies; is there one you would recommend if I decide to change? In the old old days I used to like the Cerriani MX and RR front ends; but that was 30 to 35 years ago. I have heard mixed reviews (all hearsay on the internet) of the Storz Cerriani front fork but nothing concrete from anyone who has one. I do know that I would not be able to use my stock FXDXT fairing; and I don't know about any guages. That emulator, if I can find out where to get it; sounds like an affordable alternative.

Regards;

David Jackson

[Mike]

The Race Tek emulaters are available from most of the major distributors (Drag Specialties, etc.) or from us through our enternet sales dept. Works supplies a build sheet and it is a simple as filling it out, they do the rest. The Storz front end is VERY good but many do not know how to setup properly. Storz can help here or Traction Dynamics will do it for a charge if you find them at an AMA event. I believe the emulators (in your stock forks with the oil they rec.) would be fine and the Storz would be overkill (but nice). The SE fork brace is fine. You are correct in that lowering the rear increases rake but it also changes the weight bias front/rear, this in turn can cause the rear of the bike to try and drive under or around the front end when combined with weight in a saddlebag or back pak, resulting in head shake or oscillation. Of course you can go to far with this and cause head shake when the throttle is closed putting too much weight on the front end. Most road racing bikes are heavily biased to the front (large swingarm downangles) and this makes them "twitchy" on decel. Same on drag bikes but the bias is for another reason (weight transfer on acceleration when the front wheel is off the ground).
Thanks, Mike